(1). Field of the Invention
The present invention relates to a zoom finder, with a compact size and high magnification, having an Albada system.
(2). Description of the Prior Art
Recently, in lens shutter cameras, a lens mechanism provided with a bifocal adjusting position system or a zooming function as a photographing lens has become the object of attention and, with this development, a finder also having a bifocal adjusting position system or a zooming function has been required.
As examples of the finders provided with such functions for varying magnification as mentioned above, lens configurations described in Japanese Patent Preliminary Publication Nos. Sho 61-87122 and Sho 61-160712 are known. The former prior art discloses the lens configuration comprising four components of positive, negative, negative and positive shown in FIG. 1 as an optical system in which compaction has been attained, and the latter teaches the lens configuration including four components of positive, negative, negative and positive as an optical system provided with the Albada system.
The former, however, allows no introduction of the Albada system into the lens configuration of the four components. That is, in the event that the Albada system is introduced into the lens configuration shown in FIG. 1, curvature of field will be largely produced on a surface of an image side of a lens nearest to an image with the fact that a field frame is very difficult to be observed and consequently this lens configuration will have no practical use. In order to solve this problem, it is inevitable that the endmost lens component of the image side is divided into two elements as shown in another embodiment of Japanese Patent Preliminary Publication No. Sho 61-87122 and, as a result, a new problem will arise that the lens configuration is high in cost as compared with that of the four components.
Further, the lens configuration of the four components shown in the prior art of the latter, which attains the introduction of the Albada system, fails to completely reduce its total length, has a magnification ratio as small as 1.5 and forms angles of view as small as 34.0.degree..about.23.2.degree., so that, there is a problem that the lens configuration cannot meet the requirement of a wide angle necessary for the lens shutter camera.